Rate- How fast something happens, or how much something changes per nit of time; a change in quantity divided by the time it takes for the change to occur.
Motion occurs all around us. In things that we can see, like trees swaying in the wind, and even in things ona more microscopic level such as jostling atoms. However in this chapter, we will be talking about the simplist form of motion and that is along a straight-line path (Linear Motion)
2.1 Motion Relative
Relative- Rearded in relation to something else. Depends on point of view or frame of reference. Sometimes referred to as "With respect to".
When we discuss motion of an object, it is always relative to something else. Such as saying a space shuttles moves at 8 kilometers per second, we mean its movement relative to the earth below. Unless stated otherwise, when we discuss the speeds of things in our environment, we mean speed with respect to the surface of the earth. Motion is relative.
2.2 Speed
Speed- How fast something is moving; the path distance moved per time. The magnitude of the velocity vector.
Instantaneous Speed- Speed at any instant of time.
Average Speed- Path distance divided by time interval.
We see instantaneous speed when we are driving a car and look down at the speedometer. It tells us exactly how fast were going at that certain point in time. However, when planning a trip by car, the driver usually wants to know how long it will take to cover a specific distance. Since you do not drive at the same speed the whole time you would be searching for the average speed.
Average Speed = total distance covered/time interval
2.3 Velocity
Velocity- Speed together with the direction of motion.
If we say a cheetah is running at 100km/h, we are specifying just the speed. But if we say that the cheetah is running at 100km/h to the west, we are specifying the velocity. In order for an object to have constant velocity, it needs both a constant speed and constant direction.
PRACTICE
A truck speed going towards the east is 60km/h. It passes another truck that is traveling west also at 60km/h. Do both Cars have the same speed? Do they have the same velocity?
In this situation, the trucks have the same speed, however they have opposite velocities.
2.4 Acceleration
Acceleration- The rate at which the velocity is changing
The key idea that defines acceleration is change. Whenever we change our state of motion, we are accelerating. In physics, the term acceleration applies to both increasing of speeds along with decreasing. Acceleration also changes with change of direction. When your in a car riding around a curve at a constant speed, you can feel the effects of acceleration as your body moves outward towards the outside of the curve.
Acceleration = change of velocity/time interval
Acceleration (Along a straight line) = change in speed/time interval
2.5 Free Fall: How Fast
Free Fall- Motion under the influence of the gravitational force only.
Elapse Time- The time that has passed since the beginning of an event.
Free Fall Speeds of Objects Dropped from Rest:
Elapsed time
(seconds)
Instantaneous speed
(meters/second)
0
1
2
3
4
5 t
0
10
20
30
40
50
10t
We can use the letterg to represent acceleration bcause in this case the acceleration is due to gravity. g=9.8 m/s²
The instantaneous speed v of an object falling from rest after an elapsed time t can be expressed in this equation: v=gt
2.6 Free Fall: How Far
For any object moving in straight line with constant acceleration, we find the average speed the way we find the average of any two numbers. At the end of time t, the object has fallen a disance d of 1/2gt²
We use freely falling objects to describe the relationship between distance traveled, acceleration, and velocity acquired.
Whenever an objects initial speed is zero and the acceleration a is constant, that is, stteady, the equations for the velocity and distance traveled are: v=at and d= 1/2at²
2.7 Graphs of Motion
For every 1 hour, the distance is 50 kilometers. Since the object started at rest, the line starts at the origin. In this case, if we double the time, we double the distance and so forth so this particular linearity is called a direct porportion. Slope is the vertical change divided by the horizontal change for any part of the line.
Another graph for distance- versus- time is parabolic—When you double time, we do not double the distance; we quadruple it. Distance depends on time squared.
2.8 Air Resistace and Falling Objects
Air resistance affects all objects. We can notice it more in objects such as paper or feathers rather than stones or baseballs. In many cases the effect of air resistance is small enough to be neglected. With negligible air resistance, falling objects can be considered to be falling freely.
2.9 How Fast, How Far, How Quickly How Fast Changes
When we want to specify how fast something freely falls from rest after a certain elapsed time, we are talking avout speed or velocity. The equation is v=gt. When you need to specify how far that object has fallen, they are talking about distance. the equation to use in this case is d =1/2gt².
CHAPTER 2 Linear Motion
Table of Contents
2.0 Linear Motion
Motion occurs all around us. In things that we can see, like trees swaying in the wind, and even in things ona more microscopic level such as jostling atoms. However in this chapter, we will be talking about the simplist form of motion and that is along a straight-line path (Linear Motion)
2.1 Motion Relative
When we discuss motion of an object, it is always relative to something else. Such as saying a space shuttles moves at 8 kilometers per second, we mean its movement relative to the earth below. Unless stated otherwise, when we discuss the speeds of things in our environment, we mean speed with respect to the surface of the earth. Motion is relative.
2.2 Speed
We see instantaneous speed when we are driving a car and look down at the speedometer. It tells us exactly how fast were going at that certain point in time. However, when planning a trip by car, the driver usually wants to know how long it will take to cover a specific distance. Since you do not drive at the same speed the whole time you would be searching for the average speed.
2.3 Velocity
If we say a cheetah is running at 100km/h, we are specifying just the speed. But if we say that the cheetah is running at 100km/h to the west, we are specifying the velocity. In order for an object to have constant velocity, it needs both a constant speed and constant direction.
- PRACTICE
- A truck speed going towards the east is 60km/h. It passes another truck that is traveling west also at 60km/h. Do both Cars have the same speed? Do they have the same velocity?
In this situation, the trucks have the same speed, however they have opposite velocities.2.4 Acceleration
The key idea that defines acceleration is change. Whenever we change our state of motion, we are accelerating. In physics, the term acceleration applies to both increasing of speeds along with decreasing. Acceleration also changes with change of direction. When your in a car riding around a curve at a constant speed, you can feel the effects of acceleration as your body moves outward towards the outside of the curve.
2.5 Free Fall: How Fast
- Free Fall- Motion under the influence of the gravitational force only.
- Elapse Time- The time that has passed since the beginning of an event.
Free Fall Speeds of Objects Dropped from Rest:(seconds)
(meters/second)
1
2
3
4
5
t
10
20
30
40
50
10t
The instantaneous speed v of an object falling from rest after an elapsed time t can be expressed in this equation: v=gt
2.6 Free Fall: How Far
For any object moving in straight line with constant acceleration, we find the average speed the way we find the average of any two numbers. At the end of time t, the object has fallen a disance d of 1/2gt²
We use freely falling objects to describe the relationship between distance traveled, acceleration, and velocity acquired.
Whenever an objects initial speed is zero and the acceleration a is constant, that is, stteady, the equations for the velocity and distance traveled are: v=at and d= 1/2at²
2.7 Graphs of Motion
Slope is the vertical change divided by the horizontal change for any part of the line.
Another graph for distance- versus- time is parabolic—When you double time, we do not double the distance; we quadruple it. Distance depends on time squared.
2.8 Air Resistace and Falling Objects
Air resistance affects all objects. We can notice it more in objects such as paper or feathers rather than stones or baseballs. In many cases the effect of air resistance is small enough to be neglected. With negligible air resistance, falling objects can be considered to be falling freely.2.9 How Fast, How Far, How Quickly How Fast Changes
When we want to specify how fast something freely falls from rest after a certain elapsed time, we are talking avout speed or velocity. The equation is v=gt. When you need to specify how far that object has fallen, they are talking about distance. the equation to use in this case is d =1/2gt².Works Cited
http://biotsavart.tripod.com/imageTNN.JPG
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